Regarding Showdown, I asked Joim well before posting this thread how Gen 3 and Gen 4 development were coming along on Showdown. He stated both had bugs, Gen 3 more so than Gen 4, which is a large problem for tour. When both are mostly bug free, we will make the transition. I am not the biggest fan of using two different simulators for the Smogon Tour, but I may consider having BW tours take place on Showdown. Until further notice, they will still occur on PO.
As for what the next tour format will be - don't ask. It's being worked on.